In applications where large variations in thermal conditions occur in relation to heat sensitive components, it becomes necessary to control the transfer of heat in order to maintain the operational thermal environment substantially constant. This is particularly so in spacecraft applications where large temperature differentials occur when surfaces are periodically exposed to or shielded, for example, from sunlight. Accordingly, the thermal environment is controlled by such dievices as variable conductance heat pipes, louvers or the like, or by means of thermal conductance devices such as thermal switches. Thermal switches have a large or relatively large ratio of maximum to minimum heat transfer in relation to louvers and are generally preferable for many applications. A thermal switch comprises a device which is capable of providing a region of variable thermal conductance which is generally temperature actuated. Known prior thermal switches utilize a number of actuating means such as bimetals, expanding fluids or materials which undergo a phase change. While known prior art devices tend to more or less operate as intended, they are subject to degradation due to vibratory loads and wear.